This invention relates to the problem of corrosive action on metal surfaces such as aluminum, cadmium, magnesium and the like, paticularly when such metals are exposed to atmospheric pollution.
Atmospheric pollution in the form of acid rain, salt spray, chemicals such as sulfur dioxide and various particulate matter continues throughout industry to result in increasing levels of damaging corrosion on metal surfaces. It is well known that such corrosion is formed primarily from the interaction of metallic surfaces with atmospheric pollution, moisture and oxygen, particularly at elevated temperatures. Metals especially vulnerable to damaging corrosion are found in exposed climate control equipment, water cooling apparatus, and refrigeration systems with their evaporators and condensers that employ aluminum fin tubes as well as flat surfaces.
In the operation of such equipment there is a significant increase in energy costs incurred whenever operating efficiency or heat transfer coefficients are impaired by corrosion build-up or particulate deposits. Such action also clogs air passages between the fins of fin tubes. As a result, air flow necessary to dissipate or absorb heat is restricted and evaporators and condensers are unable to perform their intended functions. As operating efficiency drops, energy costs rise to a point where the need for power is continuous and the energy cost for operation is at a maximum. Should the unit continue to operate in this mode of decreased efficiency, accelerted deterioration of the exposed metal surfaces results. Costly equipment damage and shortened equipment life necessarily follow.
In the prior art, the use of a liquid chromate conversion coating as a corrosion inhibiting substance for the protection of aluminum and other metals is well known. Illustrative of such coatings are those disclosed in U.S. Pat. Nos. 4,088,621, issued May 9, 1978 to Russell C. Miller and 4,137,368, issued Jan. 30, 1979 to Russell C. Miller as well as a commercial product OAKITE L25 produced by OAKITE PRODUCTS INC. Nevertheless, prior art attempts to solve the problems outlined have not been fully successful. In some cases the protective procedures used have been unduly complicated by combining the coating with an organic resinous film. As a result, the cost of the process as well as the time required to apply the coating have been increased to undesirable levels. In other cases the protective process has been made unnecessarily complex by the sheer number of ingredients used to produce the coating. In other instances the particular mix of other ingredients with the chromate conversion coating together with the particular ingredient proportions used has caused coagulation, has produced sediment and has limited the capability of the mixture to form a uniform coating.